I'm a big fan of word games so I was drawn ot your title and stayed for the concept. Really interesting puzzle mechanic and you pulled it off really well! Reminds me of Scribblenauts but with more intentional puzzles. How did you choose words that the player could create and not? I noticed that you implemented "roof" even though I think we didn't need it to beat any of the levels.
I agree with Hotdogman287 in their suggestion below and another suggestion I have is a way to see your letters without entering the create screen. Also I thought you had to manage the amount of letters you had at once before I realized you could drag to the left and right in your letter box.